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Trane heat pump not defrosting

Thanks for your work. I have a Trane XL15i Model 41XW5038A1000BA installed last year. We live at 3500 feet with lots of snow. Have had a severe frosting problem this winter. Cut J2 jumper (per my installer) which increases defrost cutoff temp from 47 to 70 degrees, and defrost every 3 hours for 12 minutes when ambient temp less than 30. Works perfectly and no increase in KWH use compared to before jumper cut. Default is defrost to 47 degrees when ambient temp >30, regardless of whether J2 is cut. In AM when ambient temp >30 unit is heavily frosted. Per manual and discussion with installer have jumped TST to Test Common briefly to increase board timings, then jumped test common to FRC-DFT and unit defrosts. Installer changed defrost board and put in new sensors, checked charge and system operation and said there is really nothing else to do except manually defrost at the defrost board (turning on the cooling cycle at the thermostat also works, and does not turn on the resistance heater which is normally turned on to keep the house warm during the autodefrost cycle). Cools the house a little but works. I don't think the defrost cycle stays on long enough when ambient temp >30. Any suggestions how to proceed? I am not a DIY on this.

Why is your installer asking you to cut wires etc... On the system? He installed it so he sould be doing all the repairs not you!

This would be like me buying a new car then calling the dealership to report a problem and them telling me how to fix! That just doesn't make since to me? As far as DIY, although you stated you were not, you are once you started making repairs/cut wires on you system. So we can't offer advice to you. Your installer should be doing this work not you.

He is the local rep in business here for many years. You may not be familiar with this heat pump, as judged by the comments. The installation manual recommends cutting jumper J2 if there is a defrosting problem. It just cycles the defrost every 3 hours for 12 minutes rather than using the sensor, and increasing the defrost cutoff temp from 47 to 70 degrees when ambient temp is less than 30. Otherwise when ambient temp>30 operates in the usual manner with cutoff temp 47. Read the manual.